1. Field of Invention
The invention relates generally to a wellhead assembly for use subsea, and having wellhead components that align during assembly to register passages in the respective components.
2. Description of Prior Art
Subsea wellbores are formed from the seafloor into subterranean formations lying underneath. Systems for producing oil and gas from subsea wellbores typically include a subsea wellhead assembly set over an opening to the wellbore. Subsea wellheads usually include a high pressure wellhead housing supported in a low pressure wellhead housing and secured to conductor casing that extends downward past the wellbore opening. Wells are generally lined with one or more casing strings coaxially inserted through, and significantly deeper than, the conductor casing. The casing strings are typically suspended from casing hangers landed in the wellhead housing. One or more tubing strings are usually provided within the innermost casing string; that among other things are used for conveying well fluid produced from the underlying formations. The produced well fluid is typically controlled by a production tree mounted on the upper end of the wellhead housing. The production tree, which is a large, heavy assembly, is generally equipped with a number of valves and controls mounted thereon. One of the largest challenges when running and installing tubing hangers in wellheads is ensuring correct orientation to ensure proper communication with downhole equipment, and to prevent damaging the couplers and seals between the production tree and tubing hanger during installation of the production tree. Several systems have been previously employed to achieve orientation, which consume valuable rig resources.
Some subsea wellhead assemblies include a tubing hanger spool that lands on an upper end of the high pressure housing. The tubing hanger is supported within the tubing hanger spool, and can be landed therein prior to or after the production tree mounts to the upper end of the tubing hanger spool. Difficulties are typically encountered when landing the tubing hanger in the tubing spool and ensuring the tubing hanger is properly oriented so that axial passages in the tubing hanger and production are aligned.